Direct-indicating high-vacuum meter



March 2,192.6. 1,575,059

v J. CNI-5 ET AL DIRECT INDICATNG HIGH VACUUM METER Filed Feb. 5, 1925 Patented Mar. 2, 1926.

UNITED STATES PATENT QFFlCE.

JULIUS JONAS, OF MEIEIVRHOF, AND OSKAR SEITZ, OF OBERER KAPPELERHOF, BADEN, SWITZERLAND, ASSIGNORS T AKTENGESELLSCHAFT BRO\VN, BOVERI AND CIE.,

0F BADEN, SWTTZERLAND.

kDIRECT-INDICAIING HIGH-VACUUM METER.

T 0 all 1v ham it 11mg/ concern:

Be it known that we, JULIUS JoNAs, a citizen ot' the German Realm, residing at Meierhof, Baden` Switzerland, and Osimn l Sarra, a citizen of' the Swiss Republic, residing at Oberer Kappelerhof, Baden, Switzerland, have jointly invented certain new and useful Improvements in Diuect-Indicating High-Vacuum Meters, of which the `following is a specification. v y y It is known that the heat-conductivity ot a gas is constant within wide limits of pressure, but that it diminishes with the density ofthe gas in the case of a very high vacuum, approximately when the distance between the molecules corresponds to the length of their free movement so that from absolute'vacuum onwards a relation of proportion exists between the density and the heat-conductivity.

i This phenomenon allows of constructing sensitive direct-indicating high-vacuum meters having their range of sensitiveness situated in the region ot high vacua, whereas they are much less accurate in the case of low vacua. All vacuum meters of this kind hitherto known have however, certain drawbacks which render them unsuitable for purely technical use. p

The present invention has now for its object to provide an improved direct-acti ing high-vacuum meter consisting of a mercury thermometer whose tubular bulb containing the mercury is surrounded by a cylindrical tube fitted gas-tight upon it, which is in communication with the vacuum which is to` be measured, the arrangement being such that the mercury of the thermometer is heated by means of energy supplied from outside in as constant aV manner as possible.

An embodiment of this invention is illustrated by Way of example inthe accompanying drawing in which:-`

s is the thermometer bulb containingthe mercury g; Y

Z is the capillary tube in which the mercury rises when the bulb 7c is heated;

l1, is a glass tube surrounding the bulb 7i: and fused thereon in a gas-tight manner; e is a connecting tube for connecting the vacuum meter tothe vacuum which is to be measured;

'ml is a spherical enlargement at the end of the capillary tube Z;

Application filed February 5, i323. Serial No. 617,117.

connected in a gas-tight manner to the vacul um to be measured. Then electric current trom a supply of energy a, which should be as constant as possible, is led through a and and then the mercury g whereby this mercury is raised to and maintained at such a temperature as will cause it to rise in the capillary tube exactly up to' the mark c.

In 'the unheated state of the thermometer the mercury meniscus sinks below the mark It now the receiver be exhausted of air, the heat-conductivity of the air situated in the cylindrical cavity between 7L and will drop in the case ot' a high vacuum, and the mercury will finally reach the mark CZ in the ycase of the maximum vacuum that is practically attainable. The position of the meniscus is thus a measure for the degree of vacuum surrounding the thermometer bulb.

In order to avoid as much as possible yis too small, there is a great tendency for the mercury thread to break and stick. This drawback can be avoided by filling the space above the mercury with a highly compressed gas, for instance, theneutral nitrogen- This has a two-fold advantage first because the boiling point of mercury is higher under high pressure, and second, because this arrangement prevents the thread from breaking. The higher boiling point allows of employing a high heating` temperaturey of the bulb 7c, so that the influence of the fluctuation of the temperature of the room upon the correct operation ot the improved vacuum meter is negligible.

The compressioli-pressure of the gas over the mercury may amount to many atmospheres, but in order to avoid too great a strain upon the glass walls when the mercury is heated to a high temperature, it is necessary to employ the. spherical dome m which prevents any appreciable rise of the pressure. y

Instead of supplying the energy directly to the mercury in the vacuum meter, resistance wires may be employed to heat the bulb 7u from the outside, or such wires may be led through the mercury in the bulb.

The radial distan-ce of the enveloping tube it from the bulb L' must not be too great, in order that the lag of the readings of the instrument shall be kept as small as possible. It is advisable to make this distance smaller than the free-travel range orc the gas molecules under a normal degree of high-vacuum.

IIx/*hat we claim is l. In an ap aaratus for measuring high va-cua by direct indication, the combination with a mercury thermometer having a tubular mercury bulb, of a cylindrical enclosing tube itted gas-tight upon, and surrounding said tubular bulb so as to leave an annular space between said enclosing tube and said tubular bulb, a tube connecting said annular space to the vacuum which is to be measured, and means for providing an approximately constant supply olE energy for heating the mercury in said tubular bulb.

In an apparatus for measuring high vacua by direct indication, comprising the combination claimed in claim l, the tubular bulb having an elongated form and a relatively line bore so as to give to its contained mercury the form of a thin thread, and a capillary tube extending upward from said tubular bulb in which the heated mercury can rise.

3. In an apparatus for measuring high vacua by direct indication, comprising the combination claimed in claim l, the tubular bulb having an elongated form and a relatively fine bore and capillary tube extending upward from said tubular bulb, compressed neutral gas in the space over the mercury in the capillary tube, and an enlargement at the outer end of said capillary tube, whereby the occurrence ot a high con'ipression-pressure in said capillary tube is prevented when the mercury rises in the latter.

4. In an appara-tus for measuring high vacua by direct indication the combination with a mercury thermometer having a tubular mercury bulb, of a cylindrical enclosing tube itted gas-tight upon, and surrounding said tubular bulb so as to leave an annular space between said enclosing tube and said tubular bulb, said space having a radial dimension smaller than the free travel-range of the molecules of the gas in said annular space under the normal high vacuum, a tube connecting said annular space to the vacuum which is to be measured, and means for providing an approximately constant supply ot energy for heating the mercury in said tubular bulb.

5. In an apparatus for measuring high vacua by direct indication, the combination with a mercury thermometer having a tubular mercury bulb of a cylindrical enclosing tube fitted gas-tight upon, and surrounding said tubular bulb so as to leave an annular space between said enclosing tube and said tubular bulb, a tube connecting said annular s iacei to the vacum which is to be measured, and means for passing an approximately constant electric current directly through the mercury in said tubular bulb and thereby heating said mercury.

In an apparatus for measuring high vacua by direct indi ation, the combination with a n'iercury thermometer having a tubular mercury bulb, having a highly refleeting mirror-like external suriace of a cylindrical enclosing tube tted gas-tight upon, and surrounding said tubular bulb so as to leave an annular siace between said enclosing tube and said tu ular bulb, a tube connecting said annular space to the vacuum which is to be measured and means for providing an approximately constant supply of energy for heating the mercury in said tubular bulb.

7. In au apparatus for measuring high vacua by direct indication, the combination with a mercury thermometer having al tubular mercury bulb, ot' a cylindrical enclosing tube itted gas-tight upon, and sur rounding said tubular bulb so as to leave an annular space between said enclosing tube and said tubular bulb, a tube connecting said annular space to the vacuum which is to be measured and means for providing an approximately constant supply of energy for heating the mercury in said tubular bulb to such a degree as to ensure that a fluctuation in the temperature of the room in which said measuring apparatus is located, shall not have any appreciable e'ect upon the correct operation or' said apparatus.

In testimony whereof we have signed our names to this specification.

J ULIUS JONAS. OSKAR SEITZ. 

